1. Field of the Invention:
This invention relates to a secondary battery using nonaqueous electrolytes in which an electron donor such as lithium, sodium, etc., and an electron acceptor such as halogen compounds, etc., are used as a charge carrier (i.e., an active material).
2. Description of the Prior Art:
In recent years, attention has been paid to secondary batteries that use light metal such as lithium, sodium, etc. However, the practical application of a simple metal such as lithium, sodium, etc., to secondary batteries is very difficult. A simple metal used for the anode, after only a couple of cycles of electrical charge-discharges, grows dendrites which cause damage to the separator that electrically separates the anode from the cathode resulting in internal short-circuits. In order to solve this problem, metal materials such as Wood's metals with low melting points and organic materials such as graphite have been found to be able to be doped or undoped more efficiently with metal atoms such as lithium etc. However, when the above-mentioned materials are used for electrodes, a process by which these materials are deposited on an electrode substrate functioning as a current-collector becomes necessary. When metal materials such as alloys with low melting points, e.g., Wood's metals, are deposited on the substrate, a flux must be used as an adhesive adhering the metal materials to the substrate, which caused a decrease in the electrode capacity. Moreover, the flux must be removed by a washing process that necessitates a succeeding drying process, which is troublesome. Moreover, when organic materials such as graphite are deposited on the substrate, supplementary materials such as a binding agent, etc., in addition to a charge carrier, are required to adhere the organic materials to the substrate, which also causes a decrease in the electrode capacity.
On the other hand, activated charcoal or active carbon can be employed for the above-mentioned anode. However, the activated charcoal or the active carbon has a laminated structure with hexagonal networks made of carbon atoms. The lamination is irregularly formed, so that the activated charcoal or the active carbon cannot be doped with ions, but electrical doublelayers can only be formed at the interface between the active a charcoal or the active carbon and the electrolyte. Accordingly, when the activated charcoal or the active carbon is used as an anode material, the doping thereof with cations such as lithium does not take place and an electrical capacity corresponding only to the amount of ions stored in the electrical doublelayers is obtainable.
Carbon materials such as graphite having hexagonal networks of carbon atoms that are regularly disposed can be also used for the anode. They have a layered structure in which a plurality of carbon layers with hexagonal networks are laminated. The interlayer separation of the carbon layers into which dopants (i.e., active material ions) are introduced is as small as 0.3354 nm and the carbon layers are regularly laminated, which minimizes the amount of ions to be doped at around ordinary temperatures.